The present invention concerns a procedure for controlling the drilling management functions of a whole profile rock drill apparatus, such as the speed of rotation and the feed force of the drill bit so that the rate of penetration of the drill bit reaches its maximum setting, in which whole profile rock drill apparatus the part of the drill bit penetrating into the rock consists of cutters rotatably carried by the aid of an axle at right angles to the direction of penetration. This type of drill apparatus is represented e.g. by the tunnel drill apparatus used in the making of tunnels and by the rising rock drills, which are used to produce vertical shafts in mines for ventilation, ore transporting, etc.
When rock is being drilled with a full force apparatus, the result, is influenced by structural circumstances, by the guiding and control measures and by the characteristics of the rock itself. The rock breaking, that is the rate of penetration, depends on the spacing of the hard metal pins on the conical bits, on their shape, on the dimensions of the bits and of the available power and feed force. If these characteristics are appropriate, then the rate of penetration is substantially dependent on the control measures exerted on the apparatus. In order that the best rate of penetration might be achieved, the hard metal pins should enter the rock with their entire length, and the cutting head should have an appropriate speed of rotation and torque. The rate of penetration is acted upon by controlling the feed force and the speed of rotation.
IN WHOLE PROFILE ROCK DRILL APPARATUS OF PRIOR ART THE DRILL BIT FEED FORCE AND SPEED OF ROTATION HAVE NOT BEEN AUTOMATED, AND THE DRILL OPERATOR CONTROLS THEM IN THE BEST POSSIBLE MANNER WITHIN HIS SKILL TO REACH THE MOST ADVANTAGEOUS RATE OF PENETRATION OF THE DRILL BIT. If the feed force is too low, the points of the spikes on the cutting head rolls enter the rock only partly. If on the other hand excessive feed force is applied, the whole roll is urged against the rock with unnecessary force, whereby its bearings are subjected to high stress. The drill bit feed force is most advantageous when the spikes on the drill bit rolls just enter the rock with their total length and break stone in a depth which equals the length of the spikes. In that case the flat surfaces of the roll are not urged against the rock and bearings are not unduly stressed. It is exceedingly difficult however to exercise such control that this optimum condition is maintained: the drill operator has no means to tell how the drill bits are operating at any given time. A further interfering factor is the hardness variation of the rock.
Attempts have been made to solve this problem by fitting the drill bit with pressure transducers and feeding the information from these into a data processing unit. All such attempts have failed, however, because there is no kind of pressure transducer which tolerates the conditions prevailing in connection with the drill bit. The object of the present invention is to solve the problem in an entirely new way. Furthermore, when pressure transducers are used the only information that is gained is the hardness of the rock, and this is not directly proportional to the drillability. In the invention the idea has been realized and utilized that when the drill bit feed force and speed of rotation have been adjusted to optimum, the rate of penetration of the drill bit is also highest. The invention is characterized in that during the drilling operation the change with reference to time of the rate at which the drill bit enters the rock is measured, and the drill control actions are controlled on the basis of this change so that the drill bit feed force is controlled either to be increased or to be reduced. In a manner of speaking the procedure of the present invention continuously employs the change of the penetration rate to measure the drillability of the material that is being drilled, but this requires no expensive and vulnerable pressure transducers. Moreover, the procedure can be easily automated, whereby the feed force and speed of rotation of the drill bit of the apparatus are always maintained at their most favourable setting or in other words the rate of penetration of the drill bit is mantained at its optimum setting.